Stellar Populations and Velocity Dispersions of Ten Nearby Galaxies

Citation

Williams, Theodore Burton (1976) Stellar Populations and Velocity Dispersions of Ten Nearby Galaxies. Dissertation (Ph.D.), California Institute of Technology. doi:10.7907/85S6-PX78. https://resolver.caltech.edu/CaltechETD:etd-09052008-132346

Abstract

NOTE: Text or symbols not renderable in plain ASCII are indicated by [...]. Abstract is included in .pdf document. Previous attempts to synthesize the stellar populations of galaxies using unconstrained best fit algorithms yield astrophysically unreasonable models. Numerical experiments are performed which indicate that this behavior is due to noise in the data. Best fit models, constrained or not, are insensitive to the actual galaxy stellar population. Spectra from 3800 [...] to 6800 [...] with resolution of 2 [...] have been obtained for 137 stars, 5 globular clusters, and the nuclear regions of 10 galaxies. Line indices measured for 74 absorption lines and bands are presented. A method for determining parametrized stellar population models is discussed, and is shown to be stable in the prescence of noise. Population models and error estimates are derived for the ten galaxies. Most of the models have significant contributions from M giant stars and from metal poor stars. Only two of the galaxies seem to contain stars with metal lines stronger than those of stars in the solar neighborhood. Three of the ellipticals show evidence of recent star formation, possibly due to infall of gas from nearby spirals. The galaxies studied here can be divided by morphological type into three distinct population groups; E0 - Sa, Sb, and Sc. Velocity dispersions have been derived for the nuclear regions of the galaxies. These dispersions are estimated by comparing broadened composite stellar spectra with the galaxy spectra. The composite spectra give systematically lower velocity dispersions than those estimated from fitting with single stars. Mass to light ratios are derived from the velocity dispersions. These mass to light ratios are low, and there are no systematic differences between the nuclei of spirals and ellipticals.

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